The present invention relates generally to computer networks. More particularly, this invention relates to the measurement of network performance.
Communications systems, such as packet networks, are used in various applications for transporting data from one user site to another. At a transmission site in a packet network, data is typically partitioned into one or more packets each of which includes a header containing routing and other information relating to the data. The network then transports the packets to a destination site in accordance with any of several conventional protocols known in the art, such as Asynchronous Transfer Mode (ATM), Frame Relay (FR), High Level Data Link Control (HDLC), X.25, etc. At the destination site, the data is restored from the packets received from the transmission site.
The nature of packet switched technology, however, complicates the ability of an Information Technology (IT) manager of an end-user network to monitor the performance of a wide area network (WAN) service provider. The WAN service provider administers a WAN used for transporting data packets originating from customer premises equipment (CPE) in the end-user network across the WAN. Both the customer and the network service provider have an interest in monitoring the performance of the WAN in order to corroborate that the performance comforms with the quality of service xe2x80x9cguaranteedxe2x80x9d by the WAN service provider.
For example, one type of end-user network is an Internet Protocol (IP) Virtual Private Network (VPN). A VPN includes a set of Virtual Private Links (VPLs), each of which is a communication channel between two customer networks.
Network performance guarantees have emerged as a means for IT managers to ensure that their critical businesses data is delivered in a reliable, consistent manner. The term Service Level Agreements (SLA) refers to these performance guarantees. Common SLA parameters (or metrics) include packet throughput, packet loss ratio (PLR), packet delay, packet jitter, and service availability.
A Measurement Point is the boundary between a host and an adjacent link at which performance reference events can be observed and measured. A source Measurement Point and a destination Measurement Point are two Measurement Points at which packet traffic is measured. The traffic measured flows between the source and destination Measurement Points, but may originate before the source Measurement Point and may terminate after the destination Measurement Point.
The difference between the packet counts at a source Measurement Point and a destination Measurement Point divided by the packet count at the source Measurement Point for a measured interval of time defines the PLR. The service availability parameter, defined as the percentage of time that the IP service is available, depends on the PLR. One basis for the service availability function is a threshold on the PLR performance. The IP service is available on an end-to-end basis if the PLR for that end-to-end case is smaller than the threshold defined by the customer.
Packet delay is defined as the amount of time it takes for a packet to travel from the source Measurement Point to the destination Measurement Point. The differences between delays for a pair of consecutive packets that are observed at source and destination Measurement Points constitutes a packet jitter metric.
The primary objective of any service provider is to provide a quality service to its customers. Achieving a desired level of quality is not an easy task in light of the complexity of existing network environments. A network environment includes different types of equipment with different types of statistics for measuring performance, making difficult the measurement and correlation of end-to-end statistics.
Existing SLA monitoring devices monitor and collect statistics with respect to a specific technology (e.g., FR) or layer. Such devices, however, do not offer the capability of correlating IP statistics measured at two different points of an IP network that are separated by multiple lower layer networks. Knowing the SLA metrics with respect to a FR network (i.e., a WAN) is not sufficient for reporting end-to-end SLA metrics for a VPN that connects two CPE""s.
FIG. 1 illustrates a network 100, which incorporates one such SLA monitoring device. The network 100 includes two CPE""s 102 and 104, two Passive Monitors (PMs) 112 and 114, two FR networks 106 and 108, an IP/ATM network 110, two routers 1000 and 1002 and a Data Analyzer (DA) 116. As shown in FIG. 1, the network 100 includes clusters of technology domains (e.g., ATM, FR), which make up the paths for the VPN. The network 100 of FIG. 1 only shows two nodes of the VPN, namely CPE1102 and CPE2104. Each CPE 102 and 104 has an associated, distinct set of IP addresses.
A VPL is established between CPE1102 and CPE2104, which are considered end-points of the VPN. Consequently, end-to-end network performance statistics refer to the measurement of the PLR, delay, etc., associated with packets transported from one CPE to another. Although the VPL uses a particular protocol, such as EP, for supporting communication between the two CPEs, the IP packets constituting the VPL can be transported from a CPE to another CPE via intermediate networks that use various lower layer protocols. FR networks 106 and 108 and IP/ATM network 110 exemplify such intermediary networks in the network 100 of FIG. 1. The IP/ATM 110 network refers to either an IP network or an ATM backbone network. Routers 1000 and 1002 are used to connect the IP/ATM network 110 with the FR networks 106 and 108 respectively. The IP/ATM 10 network may include IP routers (not shown).
The PMs 112 and 114 are devices that tap into the network at two different Measurement Points, MPA and MPB, to capture FR signals. These PMs are referred to as passive monitoring devices because they collect and store the captured data without changing the packet flow.
The DA 116 is a management console that runs on a PC platform and performs analysis of the data collected by the PMs 112 and 114. The DA 116 produces reports that include SLA metrics associated with the FR network 106. The DA 116 bases the reports on the analysis of the collected data.
The PMs 112 and 114 tap into the FR network 106 through T1 monitoring jacks. The DA 116 is connected to each of the PMs 112 and 114 via an Ethernet network. Once the PMs 112 and 114 capture and store the FR signals, the PMs 112 and 114 send the collected information to the DA 116.
As mentioned above, the DA 116 produces SLA reports for FR traffic statistics, as opposed to IP level traffic statistics. That is, frames are used as the basis for performance measurement, not IP packets. Although not shown, the FR network 106 is also capable of carrying non-IP traffic in the frames. Knowing the SLA metrics with respect to a FR network (e.g., FR network 106), however, is not sufficient for reporting end-to-end SLA metrics for an IP VPN that connects two CPE locations that are on different access networks. PM 114 cannot be relocated to FR network 108 (i.e., between the FR network 108 and the CPE2104) to measure end-to-end statistics based on Frame Relay information because the Frame Relay network is not end-to-end. The frames transported on the FR network 108 are not the same (i.e., they have different headers) as those transported on FR network 106.
Although there are PMs available in the market for monitoring IP traffic (rather than just frames or ATM cells) and for enabling the DA 116 to produce SLA reports for IP level traffic statistics relevant to the performance of the VPL established between CPE1102 and CPE2104, there still would not be any correlation of IP information at different points of the VPN. The correlation of network statistics is desirable because it allows for scalability in the network 100. That is, correlation of statistics opens the possibility to place any number of PMs at any point in the network in order to obtain end-to-end SLA metrics for a VPN that connects more than two CPE locations. Therefore, there is a need in the art for a performance measurement system that allows the measurement of end-to-end SLA metrics by correlating SLA statistics collected at any two points in a network, which may include a plurality of sub-networks.
Accordingly, it is an object of the present invention to meet the foregoing needs by providing systems and methods for measuring network performance.
Methods and systems consistent with the present invention measure network performance by dividing a stream of packets flowing through a first point into logical frames, where the first point is any point in the network that supports a packet flow. Such methods and systems capture information about the packets in xe2x80x9cpackagesxe2x80x9d corresponding to the frames and correlate the contents of each package with packets flowing through a second point, where the second point is any point in the network that supports the packet flow. Network performance information is then calculated based on the correlated packages.
Both the foregoing general description and the following detailed description provide examples and explanations only. They do not restrict the claimed invention.